Cleaning process



Patented Oct. 8, 1935 CLEANING PROCESS Arthur L. Koch, Upper Darby, Pa., assignor, by mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application December 23, 1932, Serial No. 648,549

6 Claims. (01. 87-5 This invention relates to a cleaning process in which dirt, as well as grease and other soluble materials may be removed from the surfaces of articles, such as castings, stampings, and the like,

and more particularly to processes for carrying out cleaning and degreasing operations with economy and celerity.

In manufacturing, as, for example, such wares' as silverplate, enamelled name plates, razor l0 blades and a host of other articles, the processes require that the article be absolutely clean and free from grease. For example, in plating silver, the articles must first be thoroughly cleaned. If the surface is not perfectly cleaned, the plating 15 will be uneven, spotty, and will, at times, have a tendency to crack and peel. In other cases, for

example, the manufacture of machine screws, it

is desirable to remove any accumulated dirt' or dust, but to leave a film of oil to prevent corrosion. 20 Many methods of removing grease are well known and widely used. Probably the most successful of these is the method which comprises creating and confining a bath of hot vapor solvent within an open dip tank and plunging a cold 25 article within the hot vapor. As a result, solvent vapor condenses upon the article, completely absorbing and removing all traces of grease. However, dirt and other non-soluble materials often remain on the article. .Heretofore, the only way to remove this troublesome accumulation has been to dislodge the dirt mechanically, the most usual method being physical scrubbing. Obviously, this scrubbing step is troublesome, costly, and ineflicient. 35 An object, therefore, of this invention is to provide methods of degreasing plus cleaning, which will eliminate the necessity for scrubbing or similar dirt removal operation.

Another object of the invention is to provide a physical, as well as a chemical cleaning of an article solely by resort to immersion in fluids.

Another object of the invention is to provide inexpensive apparatus, free of moving parts, or complicated structure, and adapted first to absorb grease and then to dissipate residue without aid of mechanical means.

A feature resides in the fact that'by the addition of a relatively small, cheap container, and in some cases, an extra heater, present vapor degreasing equipment can be converted into a complete cleaning plant.

Another feature resides in the provision of two open containers, one of which contains a bath 55 of solvent in vapor form, the other containing a bath of solvent in liquid form, said solvents having different boiling points.

Other objects and features, relating to my methods of operation and to design, utility and economy of construction and operation of appara- I tus adapted to carry out the methods of my in-- vention, will be more apparent from the description and accompanying drawing in which:

Fig. 1 is a sectional elevation, on line l--l of Fig. 2, of one form of apparatus designed to carry out the objects and embodying the features of my invention;

Fig. 2 is a sectional elevation, on the line 2--2 of Fig. 1, and;

Fig. 3 is an elevation, partly in section, of an apparatus adapted to carry out certain phases of my invention, either when used alone or when used in combination with the apparatus of Figs.

1 and 2.

Referring now to the drawing, and with particular reference to Figs. 1 and 2, numeral 5 represents a tank open to the atmosphere at 6. The tank 5 may be constructed of any suitable material. The base of the tank 5 comprises a reservoir for a volatile solvent 1. The solvent used is determined by the type of oil or grease to be removed. Applicant prefers, and his unit is particularly adapted, to utilize a solvent whose vapor is heavier than air. For example, the chlorine substitution products of the methane and ethylene families have been utilized and excellent results obtained. Heaters 8, in the base of the tank 5, are provided to supply heat to the solvent for the generation of vapor. The heaters illustrated are of the electric immersion type, although steam coils or flame devices may be used with equal facility.

An opening 9, in one side of the tank, and near the top thereof, gives access to a condensing chamber ID. A series of cooling coils ll, preferably finned to increase their heat transfer surface, are mounted within chamber l0 and are supplied with cold water or cooling medium from any desired source. A suitable conduit [2 connects the chamber In with the solvent reservoir in the base of tank 5.

, Mounted on a bracket l3 at one end of tank 5 is an open container M, in which is a second solvent IS. The solvent I5 may be of the same general character as the solvent 1, but it should have a lower boiling point, usually somewhat less than that of solvent 1. The container [4 is mounted in such a position that it will absorb heat from the hot vapors in tank 6. If desired,

the container l4 may be provided with a separate heating means. liquid in container It may be heated by an electric heater I6, of the same general type as the heaters 8. If a separate heater is used, it should be of such capacity as to keep the liquid just below its boiling point, or it may be provided with a thermostatic control to accomplish this.

In operation, heaters 8 cause the solvent 1 to boil, thereby generating hot solvent vapor within tank 5. As the vapor level rises, assuming that a solvent whose vapor is heavier than air is used, the vapor will spill through opening 9 into chamber In, where it contacts cooling coils II and is condensed. The resulting condensate drains through conduit 12 into the reservoir in the base of tank 5, where it is regenerated into vapor by contact with heaters 8. Thus, by pro-.

the condenser is shown on one side of the tank,

and in a separate chamber, cooling coils may be provided directly on the inner surface and extending circumferentially of tank 5, or otherwise, for preventing escape of vapor to the outer atmosphere.

When an object to be cleaned, represented by numeral I8, is plunged into tank 5, hot solvent vapor condenses upon its surfaces; and absorbs oils and greases thereon, the condensate then draining off and falling by gravity to the base of tank 5. As article l8 absorbs heat from the vapor, the, condensing action decreases, and when the article approaches the temperature of the bath, the action discontinues entirely, leaving;

base of tank 5 is regenerated into solvent vapor by the heaters 8, that is, the solvent is constantly distilled in the base, since the boiling point of the solvent is much less than the boiling point of the grease. In this manner, a supply of clean, pure solvent vapor is constantly available. a

The above described step in the process is primarily a degreasing operation; and although the article, when removed from the vapor bath is dry and greaseless, a film of dust-and dirt usually remains on the surface. To remove this, the article, at approximately the temperature of the hot vapor bath, is plunged into container l4. As hereinbefore pointed out, the liquid in container I4 is a solvent of the same general character as the solvent 7, but, preferably, has a lower boiling point. In some cases, however, it may be desirable to use the same solvent bath in tank 5 and in container I4. Further, as heretofore pointed out, the liquid in M is maintained in liquid condition at a temperature near its boiling point. Therefore, when the hot article is plunged within this second solvent, its heat is sufiicient to cause a violent boiling action proximate the surfaces of the article. The resulting ebullit'ion of gas bubbles on the surface of the article is sufficient to dislodge the dirt, which falls to the bottom of container l4 and may be removed at desired intervals in any convenient manner.

As a final, and optional, step in the complete AS shown in Fig. 3, theaoiaa'ra 1 process, the article may be again plunged within the hotvapor bath for the purpos of insuring that all grease is removed, and for the additional purpose of completely drying the article, but for this purpose, a vapor bath of either solvent or 5 ing coil I I at, or near,"the top of container H,

as shown in Fig. 3. This coil, when supplied with cooling fiuid, will condense and recover the solvent vapor created by the boiling action. 15 Furthensuch a coil will minimize the loss of solvent due to natural evaporation and convect on.

Even though some articles of manufacture require that a film of oil be left on the surface to prevent corrosion, it is usually preferable in those cases, too, to remove the heavy. oils and greases as well as the dirt and to recoat the articles with i an oil.

In the majority of cases, the film must be of a desired thickness, and must cover the article uniformly. The protective film, in prior practice, has been applied either by brushing, or by dipping. If the brushing method is used, there is no way to secure a uniform coat covering every portion of the surface. If the dipping method is used, the thickness of the film cannot be controlled. In both cases, an excessive quantity of oil is used. Applicant has found that by the addition of an oil of desired character to the solvent in container l4, this result is accomplished. Further, applicant has found that by varying the ratio of oil to solvent, the thickness of the film produced may be varied. Hence, for articles which require a thin film, the ratio of oil to solvent is small, whereas if a thick film is required, the ratio is increased. However, for any given article, the ratio is maintained constant and the resulting film is uniformly constant. Not only is the final film produced by applicants method more uniform, but because of this uniformity, a substantial saving in the amount of oil used is obtained. The article is first degreased in the vapor bath in the same manner as was previously described. Then, the hot article 0 is plunger into the liquid of container I 4, to which has been added an oil. The violent boiling and ebullition occurs just as in the previous case, thereby dislodging and removing the dirt. However, when the article is removed from the container, the solvent evaporates, leaving a coating of the oil thereon. Of course, the article, in this case,,is not subjected to a second immersion in the hot vapor bath.

In some cases, it will not be necessary to have both the vapor tank and the liquid bath. For example, an article to be cleaned may be heated in any desired manner, and plunged directly into a container such as IA. The solvent action of the liquid in combination with the dirt removal action of the boiling liquid may be suflicient. However, it is evident that the solvent must be frequently changed, and, if desired, the grease laden solvent recovered as by separate distillation.

Container I4 is shown positioned at the top of tank 5, in order that radiation from the vapor in tank 5 may be utilized for heating the solvent in [4. However, no limitation with respect to the location or construction of this or other parts of the illustrative apparatus is intended, and any 76 arrangement of apparatus embracing a vapor degreasing step in a vapor bath, followed by an immersion step in a liquid bath for effecting residue removal, is deemed to be within the purview hereof.

What I claim is:

1. The method of cleaning and degreasing metal articles which comprises heating a volatile liquid solvent for oil and grease to a temperature near-its boiling point, heating the article to a temperature greater than the boiling temperature of the solvent, and immersing the article within the liquid.

2. The method of cleaning a metallic article which comprises the following steps; plunging a relatively cold article into a vapor bath of a solvent for oil or grease, plunging the article into a liquid bath of a solvent for oil or grease, having a boiling point lower than the temperature of said serving coating on a metal article which comprises heating the article, plunging the article within a liquid mixture of solvent and a preservative oil, the temperature of the article being greater than the boiling point of the solvent, removing the article from the liquid, and then permitting the solvent to evaporate.

4. The method of cleaning and degreasing a within a liquid bath of a second solvent for oil 5 or grease, thereby causing ebullition of the liquid on the surface of the article, the boiling point of the first solvent being higher than the boiling point of the second solvent. I

5. The method of cleaning and degreasing a 14} metal article which comprises degreasing the article by condensation of vapor of a first solvent for oil or gr'easeupon the surfaces of the article, cleaning the article by immersing the article within a liquid solvent for oil orgrease to cause ebulli- 15 tion of the liquid proximate the surfaces of the article, and drying the article by immersion within a second solvent vapor bath, the temperature of the first solvent bath being greater than the boiling point of the liquid solvent. go

6. The method of cleaning and degreasing a. metal article which comprises degreasing the article by causing condensation of the vapors of a first solvent for oil or grease upon the surfaces of the article, immersing the article within a 25 second solvent for oil or grease in the liquid state to cause ebullition of the liquid upon the surfaces of the article, said second solvent having a boiling point lower than the boiling point of said first solvent, and then drying the article within a 30 vapor bath of said second solvent.

ARTHUR L. KOCH. 

